1. Field of the Invention
The disclosure relates to a gray scale voltage generator, a method of generating a gray scale voltage and a transmissive and reflective type liquid crystal display device using the same.
2. Description of the Related Art
The liquid crystal display (LCD) device includes a lower substrate (or thin film transistor substrate), an upper substrate (color filter substrate) and a liquid crystal layer interposed between the lower and upper substrates. A common electrode and color filters are formed on the upper substrate. Thin film transistors and pixel electrodes are formed on the lower substrate. A voltage is applied to the lower and upper substrates, an electric field is formed between the lower and upper substrates, the alignment angle of liquid crystal molecules is changed, the transmissivity of the liquid crystal layer is regulated, and thus an image is displayed.
The liquid crystal display device is divided into a transmissive type liquid crystal display device and a reflective liquid crystal display device whether or not the liquid crystal display device employs a light source such as a backlight. A transmissive-and-reflective type liquid crystal display device is operated both in a transmissive mode and in a reflective mode.
Since optical characteristic of the conventional transmissive-and-reflective type liquid crystal display device vary according to the transmissive or reflective modes, when the conventional transmissive-and-reflective type liquid crystal display device has a superior optical characteristics in a transmissive mode, the conventional transmissive-and-reflective type liquid crystal display device has a inferior optical characteristics in a reflective mode, and vice versa.
When the cell gap of the liquid crystal layer and the twist angle of the liquid crystal molecules is fixed so as to provide an optimized transmissivity and contrast ratio in the transmissive mode, the liquid crystal display device provides an inferior reflectivity and contrast ratio in the reflective mode such that the liquid crystal display device may not provide a satisfactory display quality.
In addition, the voltage-transmissivity (V-T) curve and voltage-reflectivity (V-R) curve depending on voltage shows different characteristics according to the mode such as transmissive mode or the reflectivity mode. Accordingly, when the liquid crystal display device employs a same gray scale voltage generating circuit both in the reflective mode and in the transmissive mode, the display quality of the liquid crystal display device may be deteriorated.